A control panel can be connected a device (e.g. computer) and used as a method of physical interaction with the device. There are many applications where a control panel can be used, for example, sound and light applications (e.g. stage lighting, video editing, keyboards, DJ equipment), cars, factory equipment and machine controls.
A typical control panel is made up of controls such as knobs, faders buttons and display devices such as markings or legends, light emitting diodes (LED) or LCD displays. When a knob or button is moved, the control panel generates data which the device recognises, in turn, the control panel receives data from the device and displays information on its display devices. Control panels tend to be constructed using materials and techniques that make it difficult to change the appearance of the control panel after manufacture. As a result control panels are typically designed for one specific application so that the controls directly suit the device under control.
There are many situations where it is desirable to change the appearance of a control panel either after manufacture or during use. One example is when control panels are used in conjunction with audio software applications to emulate the control surface of a mixing desk. A typical audio software application has many functions and making a hardware control for every function parameter is impractical due to the high cost and amount of space that would be required. There are many examples of prior art that solve this problem by providing a small number of hardware controls that can change different software parameters dependant on the current mode of operation. However, the use of a control knob to adjust multiple parameters can lead to the following difficulties;                Control knobs typically have a visual indicator such as a line marked onto the knob so the user can tell the controls current position or value. This line cannot be updated by software and therefore when a control knob is used to represent multiple parameters, the line often becomes out of sync with the software parameter. Consequently, this visual indicator is not usually included. As a result it is difficult to know what the current position of the control is. This issue has been partly solved by providing a ring of LED's around the control knob, however, a ring of LED's only provides an approximate indication of the control knob's position and for many applications this is not accurate enough.        A control knob typically has an associated scale (a set of ordered marks at fixed intervals used as a reference), and legend (name, title, unit of measurement etc . . ). Legends and scales surrounding hardware controls are usually painted or engraved onto the panel during manufacture and therefore cannot be changed at a later date. As a result any legends and scales have to be designed in a way that is appropriate for all parameters that the control knob intends to represent, this results in a generic and un-informative control panel. Consequently the user can find it difficult to know what each hardware control is currently controlling. Some control panels have partly solved this difficultly by providing a small LCD display next to the hardware control. The LCD display can show the control name, however, the scale cannot be changed. Other controls panels have partly solved this problem by locating controls close to, or over a large TFT display, however non-transparent connections are required to make the controls work and these connections obscure part of the screen from view.        Software applications are often changed and updated. It is difficult to adapt any related hardware after it has been manufactured.        It is difficult to design control panels that can be used for multiple devices or software programmes.        
The following prior art, as described below, has partly solved some these difficulties, however some difficulties remain unsolved.
From U.S. Pat. No. 5,777,603, a device is known with a flat panel display which facilitates operation of one or more electrical circuit control devices. A rotatable and/or push able operated knob is attached to the face of the display within the image area of the display. The display has a light transparent zone within the image area which extends to the back of the display to enable photoelectric detection of the knob. Light is transmitted upwardly through the control knob and then is reflected downwards within the control knob to a detector. However this is contingent on a optical path through the display which has a number of disadvantages;                The construction of such a display would be expensive, especially for large screens;        A low cost, readily available, mass produced display could not be used;        A control panel could not be retro-fitted to a system or computer where a standard screen already exists.        No monitor containing a cathode ray tube can be used;        
From patents US 2009/015549 A1 and EP1501007 A2 a device is known for accepting a user input comprising a display, a plate, a control knob positioned over the display, a light detector and a light emitter. The control knob comprises reflective stripes and the light detector is positioned to detect light reflected by the reflective stripes, the light beam reflects off the outer surface of the control knob. However this method of detecting movement, using reflective stripes, has the following disadvantages;                It is not possible to arrange a large array of control knobs over a display such that one control knob does not interfere with the photoelectric detection of a second control knob; In applications such as audio mixing equipment it is advantageous to have many high resolution control knobs located in the smallest space possible. If this reflective method is deployed and many control knobs are positioned over a display, unintended reflections will occur making it difficult to detect which control knob is moving. This is particularly apparent when control knobs are positioned close together.        The accuracy (or resolution) at which angular displacement of the control knob can be measured is not high enough for many applications. The achievable resolution is significantly less than a traditional potentiometer. The resolution can be increased by providing more reflective stripes, however the resolution is limited by the acceptable width of each stripe. As each strip becomes smaller less light is reflected and unintended reflection can occur. Further, if the separation distance between the control knob and the light devices is increased, the accuracy (or resolution) at which angular displacement of the control knob can be measured decreases.        A relatively large reflective strip is required in order to reflect enough light and avoid interference problems. This limitation restricts the size of control knobs such that only large control knobs can be used.        The light detector and light emitter must be positioned close to the control knob. Consequently a reflective configuration is only suitable for small displays or where control knobs are positioned close to the edge of a display. Since the proportion of light that is reflected back to the light detector, from the light emitter, decreases exponentially as the separation distance is increases, this detection method becomes susceptible to interference as the separation distance is increased;        